Serial memory device comprise memory, associated memory controller, power supply and a serial interface in a housing. These devices are intended as stand alone external devices that can be coupled with a microcontroller or microprocessor in systems where additional memory is needed to store data or program instructions that need to be stored in a non-volatile fashion. The housing can be very small because external pins are only required for power supply, the serial interface and optionally one or more address pins. The serial interface can be a serial peripheral interface (SPI) which generally only requires four external pins for bi-directional communication. Other serial interfaces may apply, such as I2C, single wire serial busses, etc. which require even less pins.
The respective protocol used depending on the serial interface defines how data is transmitted and received. To read a specific memory location, a master device must transmit a respective request to the serial memory which includes the address from which data is to be read. Once this command has been received the serial memory device retrieves the data and sends the data back to the master. In particular, in the SPI protocol, there is only a half clock between receiving the last address and streaming out the first data byte, while the read process within the serial memory device requires two full clocks at maximum frequency. Hence, the serial memory device requires substantial decoding circuitry, in particular a high number of sense amplifiers, to provide the data and meet the SPI transmission requirements. Other serial protocols may face similar timing problems.